Database Integration with Flask-SQLAlchemy

• What to learn: Connecting to a database, defining models as Python classes, and performing CRUD (Create, Read, Update, Delete) operations.

• Django Connection: This is the single most important topic for Django. Flask-SQLAlchemy (an ORM) introduces you to the Object-Relational Mapper concept. Django has a built-in, very powerful ORM, and understanding the purpose of an ORM in Flask will make Django's ORM feel intuitive.

Database Integration with Flask-SQLAlchemy

Flask-SQLAlchemy is an ORM (Object Relational Mapper) that lets you interact with a database using Python classes instead of raw SQL.
This is the same concept Django’s ORM uses — but Flask's lightweight nature helps you understand it more transparently.

1. Installing Flask-SQLAlchemy

First install Flask and SQLAlchemy inside a virtual environment:

pip install flask flask_sqlalchemy

2. Connecting Flask to a Database

In Flask, you configure the database connection using app.config.

Example (SQLite database):

from flask import Flask from flask_sqlalchemy import SQLAlchemy app = Flask(__name__) app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///mydatabase.db' db = SQLAlchemy(app)

3. Defining Models as Python Classes

A model represents a table in the database.
A field is a column.
An object is a row.

Example User model:

class User(db.Model): id = db.Column(db.Integer, primary_key=True) username = db.Column(db.String(80), unique=True, nullable=False) email = db.Column(db.String(120), unique=True, nullable=False) def __repr__(self): return f"<User {self.username}>"

4. Creating the Database & Tables

python

Then in Python shell:

from app import db db.create_all()

This generates the mydatabase.db file with a users table.

5. CRUD Operations (Core of ORM Learning)

CREATE

user = User(username="john", email="john@example.com") db.session.add(user) db.session.commit()

READ

User.query.all() # list all users User.query.filter_by(id=1).first() 

UPDATE

user = User.query.get(1) user.username = "john_doe" db.session.commit()

DELETE

user = User.query.get(1) db.session.delete(user) db.session.commit()

These simple operations teach the core ORM principles that directly transfer to Django.

Why This Topic is Critical for Django

Understanding Flask-SQLAlchemy makes Django’s ORM easier because both rely on the same concepts:

Examples:

Flask

User.query.filter_by(username="john").first()

Django

User.objects.filter(username="john").first()

Identical concept — different syntax.

Learning SQLAlchemy helps you understand:

• model relationships

• migrations

• database schemas

• how objects represent rows

This is EXACTLY what Django does behind the scenes, but more automatically.